Chapter 14 – Part 1The Digestive System

The Digestive System and Body The Digestive System and Body MetabolismMetabolism

Digestion Takes in food (ingests it)

Breaks it down physically and chemically into nutrient molecules (digests it)

Absorbs the nutrients into the bloodstream

Then, it rids the body of the indigestible remains (defecates)

Organs of the Digestive SystemOrgans of the Digestive System

The organs of the digestive system can be separated into two main groups:1. Alimentary canal – continuous coiled hollow

tube• Performs the whole menu of digestive functions

(ingests, digests, absorbs, and defecates)

2. Accessory digestive organs• Assists the process of digestive breakdown in

various ways• Includes the teeth, tongue, and several large

digestive glands

Organs of the Digestive SystemOrgans of the Digestive System

The Alimentary CanalThe Alimentary Canal

The alimentary canal is also called the gastrointestinal (GI) tract.

Continuous, coiled, hollow, muscular tube that winds through the ventral body cavity

Is open at both ends

Is about 30 feet long in a cadaver

Organs of the Alimentary CanalOrgans of the Alimentary Canal

Mouth

Pharynx

Esophagus

Stomach

Small intestine

Large intestine

Anus

Mouth (Oral Cavity) AnatomyMouth (Oral Cavity) Anatomy

Lips (labia) – protect

the anterior opening

Cheeks – form the lateral walls

Hard palate – forms the anterior roof

Soft palate – forms the posterior roof

Uvula – fleshy fingerlike projection of the soft palate

Mouth (Oral Cavity) AnatomyMouth (Oral Cavity) Anatomy

Vestibule – space between lips and cheeks externally and the teeth and gums internally

Oral cavity proper – area contained by the teeth

Tongue – muscle that occupies the floor of the mouth

Mouth (Oral Cavity) AnatomyMouth (Oral Cavity) Anatomy

Tonsils

Palatine tonsils

Lingual tonsil

Processes of the MouthProcesses of the Mouth

Mastication (chewing) of food

Mixing masticated food with saliva

Initiation of swallowing by the tongue

Allowing for the sense of taste

Pharynx AnatomyPharynx Anatomy

Nasopharynx – not part of the digestive system

Oropharynx – posterior to oral cavity

Laryngopharynx – below the oropharynx and connected to the esophagus

Pharynx FunctionPharynx Function

Serves as a passageway for air and food (oropharynx and laryngopharynx only)

Food is propelled to the esophagus by two muscle layers

1. Longitudinal inner layer

2. Circular outer layer (constrictor muscles)

Food movement is by alternating contractions of the muscle layers This propelling mechanism is called

peristalsis

EsophagusEsophagus

Runs from pharynx to stomach through the diaphragm

Conducts food by peristalsis (slow rhythmic squeezing)

Passageway for food only (respiratory system branches off after the pharynx)

About 10 inches long

Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs

Mucosa

Innermost layer

Moist membrane

Consists primarily of:

Surface epithelium

Plus a small amount of connective tissue (lamina propria)

Small smooth muscle layer

Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs

Submucosa

Found just beneath the mucosa

Soft connective tissue layer containing blood vessels, nerve endings, lymph nodules, and lymphatic vessels

Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs

Muscularis externa –

Smooth muscle layer made up of:

Inner circular layer

Outer longitudinal layer

Serosa

Outermost layer – visceral peritoneum

Layer of serous fluid-producing cells

Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs

Serosa

Outermost layer

Consists of a single layer of flat serous fluid-producing cells

Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs